The major objective of this proposal is the localization, characterization, and isolation of those proteins which are specifically concerned with the highly repeated DNA sequences in Drosophila. Special attention will be given the proteins of the nuclear port lamina complex, and to those proteins which function as sequence specific DNA binding proteins for the highly repeated sequences. Methods are proposed for isolating this class of proteins and for identifying genetic mutants of these proteins. It is proposed that the function of heterochromatin is one of organization both within and outside of the nucleus.